Walnut tree problems

Can anyone advise - we think our 50yr old walnut tree is dying! It produced quite a lot of very small leaves this spring but now they are all falling off in the hot weather. Last year the leaf canopy was reduced noticeably but not as bad as this year. Is it lack of water/a walnut tree disease/honey fungus? I took some of the small rather yellowish leaves to Hyde Hall yesterday but they didn't know what it was. The tree has been healthy and vigorous for the 35 years we've lived in the house. we have had it shaped twice now to keep it to a reasonable size for a suburban garden - the last time was in 2005,

Alas, I fear root disease is to balme here, especially honey fungus to which common walnuts are rather suceptible - the only remedy I fear will be the chainsaw. Be sure to get the roots out before replanting. Try and source a walnut grafted onto balck walnut rootstock - the black walnut is resistant to honey fungus.

Hmmmm, well Boggy - qualified opinion may disagree with your interpretation - the Pathology Lab at Wisley states that most perennials could be susceptible to one species or other of honey fungus. Whilst the advisory service at Wisley does not appear to have confirmed a case of Armillaria sp in Juglans nigra in the last decade or so this does not imply that J. nigra is immune from its ravages.

Probably more accurate to say that there is little evidence to support susceptibility rather than confirming immunity. Science should be the way forward here not hearsay or anecdote.

Well since my last post we've taken a look at what is under the bark atthe base of the trunk. The wood is damp and rotting with white stuff. It smells like mushrooms. So some sort of fungus - but how do I know if it honey fungus???

Lottie, in view of your last post this definitely sounds like honey fungus. A characteristic symptom is exactly as you describe: sheets of white fungus mycelium between bark and wood, smelling of mushrooms.

If you dig down to look at the main roots, at least some of them will be affected in the same way. The key feature is that honey fungus grows in and kills roots by forcing its way between bark and wood. After killing the root, it then feeds on the decomposing wood. When the advancing infection reaches the base of the tree it starts to encircle it and at this point you start to see symptoms above ground, just as you describe. It is too late by this stage to save the tree.

Honey fungus spreads through the soil by means of rhizomorphs, black threads which can then infect new roots on contact. However, the rhizomorphs can only live when they are attached to the dead roots they are feeding on, they do not live independently in the soil. To deal with an infection you have to do two things. Firstly, excavate all the affected roots and burn them. Secondly, try and trace where the infection came from, which is almost certainly another old stump in the near vicinity. If you can be sure you have got rid of all the roots and stumps that might be a source of re-infection, you will be safe to replant. However, it would still be safest to replant outside the root zone of the old tree, because many trees do not thrive if replanted directly where one was previously growing.

Juglans nigra would be a safer bet than J. regia in view of its strong resistance to infection. It is stated to have edible nuts, but I'll leave others to comment on how good they are, in my experience it is grown primarily for its timber.

We have had a quote for removal of the tree - just under £400 which includes £40 for grinding out the root ball. I don't know whether that will be enough to remove it all. I was hoping it wasn't honey fungus - as the tree guy din't think it was.

Well, grinding out the root will only prevent spread of fungal material if it is all removed - excessive grinding will cause lessions / root damage to neighbouring trees & shrubs potentially increasing probability of further root deterioration. This is not the end of the world - remember that RHS Wisley is riddled with honey fungus in all its guises as well as many other fungal problems - just like most gardens! If you are going to have the 'stump' ground out it is well to ensure that it is ALL ground out (not just the top 10cms or so) and that all substantial roots are also removed. Waste material should ideally be moved to a composting area and incorporated/broken down with loads of leaf/green waste. Otherwise - plant less susceptible speicies and try & attain optimal health by promoting good growing conditions!!!!

if nothing else - when the 'grinder' has finished their business - you should be able to dig to at least a forks depth without undue problems!!!!!